Described below is a method for the supply of encoded geoimage data from a server unit to at least one navigation receiver module, a geographical region being pre-defined by uncoded geoimage data stored in the server unit and at least one wireless communication interface being present between the server unit and the at least one navigation receiver module.
Navigation systems have become increasingly common in recent years. The navigation systems are frequently fixedly installed in vehicles or retrofitted as mobile navigation systems. In addition to a navigation receiver module for receiving “global positioning system” (GPS) position signals and/or speed signals, such a navigation system includes at least one display unit on which a map extract which may be based on vector graphics, for example a country map or a city map, is shown. In this connection, it is preferable that the map extract is shown in which the object associated with the navigation receiver module is currently located. Furthermore, in addition to the current position information, directional information and/or speed information may also be derived from the GPS position signals received, and possibly displayed on a further display unit or superimposed on the map extract shown.
The map data required for producing the map extract on the display unit is frequently stored on a removable data carrier, for example a DVD (“digital video disc”). The removable data carrier thus contains all the map data which is relevant for the representation of a defined geographical region, for example individual countries or regions. Using the position information determined by the navigation receiver module, the map data relevant to the map extract to be displayed is selected from the map data and shown on the display unit. The map data shown, for example, using vector graphics has in this case a sufficiently high resolution to be able to provide the user of the navigation system with a clear impression of the section of road and/or the route still to be covered.
In future navigation systems, in addition to the aforementioned navigation information, the display of geographical image data, i.e. so-called “geoimage data” is planned. Such geoimage data refers to aerial photographs of a pre-defined geographical region of the surface of the earth produced by a satellite unit, which for example in addition to the map data may be made available in a fixed manner in the navigation system and may be displayed on the display unit. As a result, the user gains additional information.
The representation of such geoimage data on the screen of a navigation system, however, requires the data to be edited and namely, in particular, the data format to be adapted to the respective configuration of the display unit provided in the navigation system. In navigation systems currently known, fixed geoimage data is exclusively used. A contemporaneous supply of current geoimage data to the navigation receiver module of a navigation system, for example in real time or merely with a slight time delay, is not able to be implemented by the known systems. A real-time supply of data frequently fails, due to the fact that the quantity of data which has to be transmitted within a very short period of time from, for example, a central server unit to a navigation receiver module arranged decentrally is too high. The transmission capacity of currently available wireless communication interfaces is not sufficient for this purpose.
For reducing the quantity of data to be transmitted, a plurality of different data encoding methods are known from the related art, in particular methods for image data encoding. Such methods for image data encoding, for example, skillfully use specific individual aspects of the image content, in order to permit almost loss-free encoding of the image data. To this end, the image content is analyzed, individual image areas being assigned to various data groups, and the various data groups respectively being subjected to variable encoding, and namely such that a representation of the image of the highest possible value in qualitative terms represented by the encoded image data is possible. Known encoding methods thus use variable coding depths, in particular for regions in which quality losses are able to be taken into account, i.e. image data which reproduces the face of a person is encoded with a higher coding depth than the image data relating to the background.